PS081 datasheet(29/155 Pages) AMSCO

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3-6

PSØ81

For Wheatstone bridges an additional external analog switch is needed. We recommend TS5A3160

because it has a good behavior even at supply voltages lower than 2.7 V. For supply voltages of 3.0 V

or higher 74LVC1G3157 is a good choice, too.

Note:

In Wheatstone mode the system looses 0.6 bit of resolution. Because of this, Wheatstone connec-

tion is only recommended for applications with long wires (> 1 m) and for first tests if you don’t want

to modify your load cell wiring.

The bridge setting is 1 (register 3, bridge[1:0] = 1).

The multiplication factors must have opposite sign, e.g. Mult_Hb1 = +1, Mult_Hb2 = -1.

If the Wheatstone bridge has a gain compensation resistor (Rspan) the standard setting for TKGain

is 0.75 (ConfigReg08). The factor 0.75 doesn’t modify the span compensation behavior of the load

cell. In any case “Mod_Rspan” has to be set to 1 (ConfigReg01, Bit 6)

To avoid reflections in the Wheatstone bridge we do strongly recommend the use of ferrite cores.

They are placed in the two lines which are connected directly to PS081. Ordinary (SMD-)ferrite cores

with a damping of 100Ohm @ 100MHz with a low DC resistance (<0.1Ohm) can be used. As a con-

sequence a lower offset drift and better EMI behavior can be expected.

Caution:

Only Wheatstone bridges with one Rspan or without Rspan (uncompensated) can be used. PICOS-

TRAIN cannot work properly with Wheatstone bridges that have two Rspan.

3.3.5

Wheatstone Bridge

Figure 3.7 Connecting a Wheaston bridge

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